MAC Carb > CMB 67 case question .

[Tom Foley]

I'm adapting a MAC Carb to the CMB case and the question is should I cut an O Ring groove in the MAC carb body like the CMB to accept the O ring or just seal the carb on with some red loctite or epoxy in sparing amounts to the immediate area around the carb neck where it pilots into the drum housing . Has anybody made this modification ? Thanks for all replies .

 

[moparbarn]

I would o-ring it, Tom. Better seal & less prone to leakage from vibration. Easier to remove later, & less potential neck & housing wear/damage due to the same vibrations. If you have the room, I think 2 o-rings (top & bottom) on the carb neck would stabilize things against said vibrations. I don't like the single non grooved o-ring setup on most .21 engines & have done this on my cmb's. Carbs stay tighter longer & the o-rings last longer trapped in their groove (-;

 

[Andy Brown]

Tom,

Just cut it flat and skip the o-ring. The body is very thin in that area. The slightest pressure from compressing the o-ring will distort the body and cause the barrel to bind.

Make sure that the surface of drum housing and the carb are very flat. You won't need any type of sealer or gasket material. I just bolt it up dry and works great. every time.

A super tight o-ring seal makes no difference on a simple dump tube nitro carb. We bolt up the MAC 67 carb on our Tiger King 27 with no o-ring, gasket or sealant and it even works flawlessly on gasoline.

 

[Tom Foley]

Good point Andy the carb body is very thin there . This engine has the cast drum housing and it appears i will have to lap it flat as the drum bushing is protruding slightly . Thanks guys !

 

[steve wood]

no need. we run a .550 on a green head,no o ring,no silicone,no nothing,no problem

 

[Tom Foley]

no need. we run a .550 on a green head,no o ring,no silicone,no nothing,no problem

Getting better by the minute !! Thanks .

 

[steve wood]

Just had drum rubbing against the carb on an 80. Factory parts. Had to grind .005 off the drum

 

[David Bryant]

Just had drum rubbing against the carb on an 80. Factory parts. Had to grind .005 off the drum

is this occuring when using the factory CMB .80HR carb on the factory CMB .80HR rear drum housing? Or while using the MAC .550ID carb on the factory CMB .80HR rear drum housing?

 

[steve wood]

Factory carb,factory bar stock housing. Not much drag,just enough to polish off the black anodizing on the carb. Could be more drag when every thing gets heated up tho. After all the bugs fixed, the twin is starting to come around now

 

[Brian Schymik]

i made a 1/16 inch aluminum spacer and it has an o ring works great no mods to carb or housing